Supported catalysts have been largely applied in the petrochemical industry field, particularly in the hydrocarbon conversion, olefin selective oxidation, selective hydrogenation and other important reaction processes, because of their excellent heat and mass transfer performance, and the feature that can achieve continuous reaction easily. Their application account for more than 70% of the total catalyst.
In the preparation process of the supported catalysts used in the important petrochemical reactions, the immersion, spray and coating methods are usually used to add the supporting metal into the catalyst. By the use of above methods, the supported metals are easy to be influenced by the solvation effect and the cluster effect of the metal during the preparation process, and it is also easy to form the aggregation of the metal microcrystal in the followed calcination process, which may result in poor distribution of the supported metal and instability of the catalyst structure, low dispersion degree of the active metal, high energy consumption and large wastage of the noble metal.
Hydrotalcite-type composition include pure hydrotalcite or hydrotalcite-like compound, the host structure of hydrotalcite usually comprises two type of metal hydroxides, therefore hydrotalcite is also known as layered double hydroxides (LDHs). The intercalation composition of LDHs can be named as intercalated-LDHs. Hydrotalcite, hydrotalcite-like and intercalated-LDHs are generally named as LDH intercalation materials. These materials feature hexagonal lamellar structure, and the LDH sheets are high rigidity; therefore it is difficult to prepare the lamellar structure with controllable morphology. LDHs are one type of inorganic materials with unique structural characteristics, such as the elemental compositions and the pore structure can be tuned in a wide range, and the types of the interlayer anions can also be designed. These features supply a basis for LDHs to become the potential catalysts and the catalyst precursors in industry.
The public patent (CN 1269260A) describes a preparation method of the supported hydrotalcite. The method involves a simple one-dropping or double-dropping process to assemble the divalent-metal-containing LDH precursor at the surface and in the inner pore of the Al2O3 carrier through a reaction of the alkaline-earth metals and soluble trivalent metal salts. The calcination product of the LDH precursor exhibit a good catalysis activity in the alcohol/ether reaction of the formation of the amyl acetate. A literature (Journal of catalysis 231(2005) 92-104) reported that Ni metal supported on the Mg—Al composite oxides can enhance its activity as a catalyst. As well, because of the isolation effect on the metal atoms induced by the ion interaction in the LDH layer, this method can also enhance the catalysis performance and the stability of the catalyst, and play a positive role in reducing the consumption of the noble metals.